The key pair mechanism + signagure, and attaching social media profiles are slightly different things. One is about cryptographic proofs, and one is about relations. With regard to relations, this is nothing new, we've been doing it for about a decade. You just add some JSON next to the pubkey. In fact nostr has done it in a pretty poor way, compared with other solutions. For example most people would use JSON for a social profile, but nostr uses stringified JSON which is hard to work with. Similarly other system are interoperable and extensible. Take website for example. You might have 2 websites, but nostr doesnt have a mechanism to add more than one website, whereas standardized methods that have existed a long time allow this optionality. Nostr just about works, but most of it was taken from things that came before.